Conventional recordable optical recording media can be divided into write-once optical recording media (WO-media) and rewritable optical recording media (RW-media). A plurality of recording materials for both types of media are known. For example, WO-media are typically realized using organic dyes, metal oxides and nitrides, or bilayers such as a Cu/Si bilayer. RW-media are generally realized using phase-change materials such as Ge2Sb2Te5 or Ag3In5Sb71Te21. Usually a single phase-change layer is used.
Though phase-change layers are typically used for RW-media, they may likewise be used for WO-media. For example, U.S. Pat. No. 6,841,218 discloses the usage of two adjacent recording sublayers of a phase-change material for a write-once optical recording medium. The first recording sublayer comprises a first composition which can be changed into another composition more stable in an amorphous state by combining with a component included in the second recording sublayer.
A further optical recording medium having two recording sublayers is disclosed in U.S. Pat. No. 5,796,708. Information marks are recorded on the medium by alloying material of the two recording sublayers using a light beam.
Still a further optical recording medium having two recording sublayers is disclosed in JP 02-156435. The medium has two layers. A first layer is a stable phase-change layer and serves as a write-once layer. Using an increased beam energy the first layer and the second layer are alloyed to form a rewritable phase-change layer. In order to enable rewritable recording in a rewritable area, an initialization step is necessary to alloy the two layers. As a result, some parts of the optical recording medium serve as a write-once area, whereas other parts of the optical recording medium serve as a rewritable area.
For some applications it would be desirable to have an optical recording medium which has write-once properties as well as rewritable properties in the same area.